No, not shut inside a sealed container. Propane is heavier than air, so a slow leak in a closed steel box settles at the floor and stays there. Full cylinders belong outside, shaded, in a ventilated and secured rack. Empty bottles with the valve open, and propane equipment with its tank pulled, are a different question and those store fine.
Almost nobody asking this is building a fuel depot. You are clearing a garage, winterizing a camper, or moving a shop into a container, and there are two grill bottles, a torch cylinder and maybe a forklift tank sitting there. The real question is whether they ride along with everything else.
The deciding factor is short: does the vessel still hold fuel. If it does, it stays outside the box. If it is genuinely empty with the valve left open, or it is an appliance you already pulled the cylinder off of, it goes in with the rest of your gear and nobody has to think about it again.
Propane vapor is denser than the air around it. Outdoors, a weep at a valve stem drifts down and disperses into the yard and you never know it happened. Inside a container, that same weep sinks to the floor with nowhere to go, because a container is built to keep weather out and it does that job in both directions.
Heat compounds it. A cylinder in an unshaded steel box gets warmer than one sitting in grass, and pressure climbs with temperature. A relief valve doing its job is meant to let vapor off into open air. Letting it off into a sealed room is the situation you are trying not to create.
Then there is what else is in there. Battery chargers, extension cords, a trouble light, a shop vac. In a normal storage container that mix is fine. It stops being fine when there is fuel vapor lying on the floor underneath it.
We do vent work in-house: roof vents, louvered side vents, cut and welded at the shop before the container goes on the truck. For stored goods, that airflow is the most useful modification on the menu.
It is not the same as turning a container into a fuel storage building. A couple of louvers does not make a box rated, approved or inspected for holding propane, and we will not tell you it does. So vents make the container a better home for the tools, hoses, regulators, fittings and the appliance itself. The fuel stays out of the discussion no matter how many we cut.
This trips people up more than the loose bottle does, because the cylinder is not what they think they are storing. It is bolted to a patio heater, clamped to a forklift, strapped to a camper tongue, or hanging off a grill they want out of the weather for six months.
Same rule, one extra step. Pull the cylinder, cap it, and put the appliance in the container. Once the fuel is off them, the grill, the heater and the machine are just equipment, and a locked steel box is a far better home for them than a corner of the yard.
We are a container dealer. We can tell you what a steel box does and does not do, and we can build vents into one. We are not the authority on how fuel gets stored on your property, and pretending otherwise would be the kind of confident wrong answer this site tries not to give.
Three quick calls are worth making. Your local fire officials, because rules on quantity and separation are set locally and genuinely differ. Whoever fills your tanks, because propane suppliers deal with this daily and will tell you straight. And your insurer, if the container sits at a business rather than a house.
If your use is a shop or a retail setup where propane equipment is part of the work, the build questions we can answer are on the workshops page and the business and retail page. Bring us the container half of the problem and take the fuel half to the people above.
Vent work is cleaner done at our Woodlawn shop than added later. Tell us what is going in and we will spec it.
Same-day reply. We'll send a real number, a real delivery window, and any photos we need to confirm fit.
You'll hear back from us today (or first thing tomorrow if it's late). For anything urgent, call (276) 237-6144.